Migrate From One Instance to Another Edited

I have my project on one instance. Now we have got another JIRA instance. (Both instance have different URLs) I want to migrate my Project from old instance to new one with all Sprints, Issues, and Backlog. Also I do not want to lose any data like comments and attachments. Also for my new instance some fields are not same. How can I maintain consistency for fields while migrating.

As far as I understand you want to migrate not a cloud instance. If you have only one Project in the instance, then it means that you want to migrate the whole instance. In this case you can follow the guide below